Recently, LCDs that are light and thin and have low power consumption characteristics have been widely used in office automation equipment, video recording and playing units, and the like. Such kinds of LCDs typically include a twisted nematic (TN) mode LCD and a super twisted nematic (STN) mode LCD. Although TN-LCDs and STN-LCDs have been put to practical use in many applications, they generally have a very narrow viewing angle. In order to solve the problem of a narrow viewing angle, IPS LCDs have been developed.
A conventional IPS LCD is shown in FIG. 4. The IPS LCD 1 includes a first substrate 11, a second substrate 12 opposite to the first substrate 11, and a liquid crystal layer 17 sandwiched between the first substrate 11 and the second substrate 12. The first substrate 11 includes a first polarizer 112, a first glass layer 110, a color filter 113, and a first alignment layer 114 arranged in that order from top to bottom. The second substrate 12 includes a second polarizer 122, a second glass layer 120, an insulation layer 127, a passivation layer 121, and a second alignment layer 124 arranged in that order from bottom to top.
A plurality of common electrodes 125 are arranged on the second glass layer 120, the common electrodes 125 being covered by the insulation layer 127. A plurality of pixel electrodes 126 are arranged on the insulation layer 127, the pixel electrodes 125 being covered by the passivation layer 121. The common and pixel electrodes 125, 126 are formed at staggered intervals. The liquid crystal layer 17 includes a plurality of liquid crystal molecules 170 that constitute positive liquid crystal. The first and second alignment layers 114, 124 are adjacent the liquid crystal layer 17, and are used for controlling the orientation of the liquid crystal molecules 170. The first and second glass layers 110, 120 are made of transparent glass material.
Referring also to FIG. 5, when a voltage is applied, the common electrodes 125 and the pixel electrodes 126 generate an electric field 18 parallel to the first and second substrates 11, 12. Because the liquid crystal molecules 170 are positive liquid crystal, the orientation of the liquid crystal molecules 170 is the same as the direction of the electric field 18. Further, in general, the liquid crystal layer 17 can absorb charged particles from its environment. Thus when the voltage is applied, the common electrodes 125 exert a first force on the charged particles in the liquid crystal layer 17 and thereby gather the charged particles, and the pixel electrodes 126 exert a second force on the charged particles in the liquid crystal layer 17 and thereby gather the charged particles.
The insulation layer 127, the passivation layer 121 and the second alignment layer 124 are located between the common electrodes 125 and the liquid crystal layer 17. The passivation layer 121 and the second alignment layer 124 are located between the pixel electrodes 126 and the liquid crystal layer 17. Therefore, the distance between the common electrodes 125 and the liquid crystal layer 17 is different from the distance between the pixel electrodes 126 and the liquid crystal layer 17. Consequently, the first force exerted on the charged particles by the common electrodes 125 is different from the second force exerted on the charged particles by the pixel electrodes 126.
Because polarities of the common electrodes 125 and the pixel electrodes 126 are always changed during the course of driving the IPS LCD 1, the number of charged particles aggregated at the common electrodes 125 and the number of the charged particles aggregated at the pixel electrodes 125 are different. Therefore, the intensity of the electric field 18 is weakened. The number of liquid crystal molecules 170 that are twisted is decreased, and the speed at which the liquid crystal molecules 170 are twisted is decreased. That is, an image delay occurs in the IPS LCD 1. Therefore the display of the IPS LCD 1 is not clear.
What is needed, therefore, is a liquid crystal display which can avoid image delay occurring and which has a clear display.